1. Field of the Invention
This invention pertains most generally to optics systems and elements, and more particularly to illumination systems within bright-field microscopes. Through the teachings of the present invention, light control within the optical path of the microscope is achieved by rotating an opaque, convex element through the light path to produce a highly beneficial contrast enhancement.
2. Description of the Related Art
Microscopes are well-known to provide magnification of small portions or samples of living or inanimate material. A sample prepared for viewing through the microscope is most generally referred to as the specimen, and may be a living biological organism, or may alternatively be other matter, whether organic or inorganic in origin. Optical bright-field microscopes, which are the subject of the present invention, magnify images formed from light passing through and about a sample for viewing of features that are ordinarily too small to be seen clearly with the naked eye. The sample may be translucent, transparent, or have some combination of varying opacity that may include opaque material as well, though with bright-field microscopes as referred to herein, the samples must have some translucence through which light may pass for viewing. The sample may also vary greatly in size, though in most instances the specimen is a relatively small sample of matter such as may be readily placed upon a carrier referred to as the slide. For those less familiar with microscopy, the slide acts as a holder substrate upon which the relatively small specimen may be supported, for transport to the microscope for viewing and, depending upon the specimen, potentially for subsequent storage or archiving. In bright-field microscopy, the slide will most preferably be of an optically transparent or translucent material, and is frequently fabricated from transparent glass.
Within the bright-field microscope, light generated by a light source is typically gathered by a collector lens and concentrated by a condenser upon the stage of the microscope. The specimen is mounted upon the stage, and the light passes through and about the specimen. The image is then magnified through a combination of objective lens and eyepiece or ocular lens, for subsequent viewing or photographing.
Bright-field microscopy is quite old, and is not limited to the inclusion of condensers or collector lenses. Prior art microscopes have been used with light-gathering mirrors and other structures that use alternative light sources such as sunlight and other natural light, as well as artificial lights that have been generated from lanterns and candles as well as electric light bulbs. As is known to those working in the field, electric light bulbs offer a particularly convenient and predictable source of light, and so today most laboratory grade microscopes include some combination of bulb, collector lens and condenser.
Various adaptations and techniques have been developed through time to enhance bright-field microscopes. A frequent goal is to improve detection and differentiation of features within a specimen. Among the more well documented methods are staining of biological specimens, illumination at oblique angles, and various contrast enhancing techniques such as phase-contrast, differential interference contrast, and single-sideband microscopy. By staining a specimen, differences in permeability and/or absorption of the stain lead to visual distinctions between various components of the specimen, and can assist greatly in the identification of the specimen. Unfortunately, once stained, the specimen is not readily returned to the state it was in prior to staining. As a result, a single specimen may not be readily analyzed by multiple methods including staining unless the staining is preserved for a last action. Unfortunately then, all other data desired to be gathered must be completely collected prior to staining, other than that derived from the staining, and no second party verification or confirmation is possible once the staining is complete. If the staining should reveal a need for further testing, absent the stain, such testing will not be possible on that sample. Particularly where samples are only available for testing in limited supply, or where independent review at different times is preferred, this drawback of staining can be quite undesirable.
Unlike staining, other methods are non-destructive and do not alter the specimen. Illumination at oblique angles produces visible reflection and refraction at the interfaces between materials having even relatively small differences in indices of refraction. Several techniques have been proposed for oblique illumination, including the use of an eccentric mount in association with the condenser aperture, variously referred to as the iris diaphragm or condenser diaphragm, and herein referred to as the aperture diaphragm. By using an eccentric mount, the aperture diaphragm may be shifted from a central position, which passes an equal amount of light from all directions about the central optical axis, to an off-axis position which only passes illumination from one side of the central optical axis through the condenser to the stage. This technique, which is discussed for example by H. N. Ott in U.S. Pat. No. 863,805, does result in a shadowcast image with improved contrast. However, resolution of smaller features within the specimen is sacrificed, and depth of field is undesirably increased due to the reduced numerical aperture of the condenser. For those less familiar with bright-field microscopes, depth of field represents the distance which is in focus along the axis of light transmission through the sample. For an infinitely thin sample, depth of field is not particularly significant. However, as one might imagine, when the sample gets thicker along the axis of light transmission, which it will in all living samples, there will be more and more features within the optical path. If many of these features remain in focus, which is what happens as the depth of field increases, then the image will become progressively more cluttered. Since a more cluttered viewing field makes identification of features more difficult, an increased depth of field is usually quite undesirable.
A similar technique is also illustrated by Ott in U.S. Pat. No. 1,501,800, as well as by Diggins in U.S. Pat. No. 2,195,166, where they each illustrate a concave-shaped oblique light diaphragm which is mounted adjacent the iris diaphragm. The oblique diaphragm includes a leaf which partially and progressively blocks light from one side of the diaphragm as the leaf rotates into the light path from one side thereof. Unfortunately, while the oblique light diaphragm is an improvement which less reduces the numerical aperture of the condenser than the earlier Ott patent, the depth of field is still increased by these Ott and Diggins inventions, and the resultant image is less than desirable. Furthermore, and as will be described in more detail hereinbelow with reference to the present invention, the concave surface illustrated by Ott and Diggins offers undesired interference in the resultant light path, which results in less contrast and a more two-dimensional image.
Rehm, in U.S. Pat. No. 3,490,828 illustrates another oblique illumination method, this time varying the light source from an on-axis mirror to a second off-axis mirror, the off-axis mirror which may be positioned for diverse angles of light incident upon the stage and specimen. While this invention offers the advantage of not significantly altering the depth of field which is in focus, thereby allowing a viewer to focus on relatively narrow vertical sections within a specimen without visual clutter, the Rehm invention requires a specially designed microscope, and may not be readily retrofit onto existing microscopes. Further, the Rehm invention does not offer advantages which are inherent in the use of diffracted light, this feature which will be discussed more fully hereinbelow with regard to the present invention. Instead, the Rehm invention is limited to oblique, full wave incident light. A similar off-axis mirror system is illustrated by Greenberg in U.S. Pat. Nos. 5,345,333 and 5,592,328, which also suffers from the same disadvantages and drawbacks.
Other various contrast enhancing techniques modify the illuminating beam, generally by altering the condenser by the inclusion of special apertures, polarizers and prisms, or half-masks. The resulting image is then filtered or modulated at the image plane of the objective lens. These techniques require several additional components and, frequently, fairly sophisticated image analyzers or electronic contrast enhancement. Examples of these are found, for example, in U.S. Pat. No. 4,407,569 to Piller et al; U.S. Pat. No. 5,394,263 to Galt et al; U.S. Pat. Nos. 5,673,144 and 5,715,081 to Chastang et al; U.S. Pat. Nos. 5,684,626 and 5,706,128 to Greenberg; U.S. Pat. No. 5,703,714 to Kojima; and U.S. Pat. No. 5,729,385 to Nishida et al. While many of these techniques offer improved image properties, the complexity and cost associated with these methods limit their application to only a few special purpose research grade microscopes. The techniques are not readily adapted to existing microscopes or lower cost student or general laboratory applications.
In a first manifestation, the invention is a combined device for enhancing contrast of a refractive specimen. The device includes a microscope having a stage for locating a specimen within an optical path, a source of light, and a means for forming an enlarged virtual image of the specimen. The microscope is combined with a convex edge plate within the optical path. The convex edge plate alters light travelling through the optical path to produce diffracted light, which illuminates the specimen. According to further features of the first manifestation, the convex edge plate is sufficiently wide that diffracted light is passed from only one edge onto the specimen, while the plate is also sufficiently narrow so as to only block a minority of light passing through the optical path.
In a second manifestation, the invention is a method for enhancing contrast of a refractive specimen comprising the steps of diffracting light within an optical pathway and defocussing the condenser lens by relative motion between the diffracting means and the condenser lens to illuminate a portion of the refractive specimen with diffracted light.
In a third manifestation, the invention is a diverging chromatic light source formed adjacent a juncture between a dark shadow and a bright field which interacts with a refractive specimen to form distinctive optical illumination maximums and minimums, in combination with an optical display for displaying the distinctive illumination as a major part of the field of view within the display.
A first object of the present invention is to provide a contrast-enhancing illumination method. A second object is to enhance contrast without altering a specimen, such that the specimen may readily be preserved unaltered for future or alternative analysis. A third object of the invention is to provide apparatus which may be placed within both new and existing microscopes at various locations within the optical path, and which is not limited to only one or a few types or brands of microscopes. A further object of the invention is to provide a low-cost apparatus which is readily purchased by owners of existing microscopes and which offers image enhancement comparable to much more costly systems of the prior art. These and other objects of the invention are achieved by the preferred embodiment, which is described hereinbelow and which will be best understood in conjunction with the appended drawing figures.